Vibrating screen



N. E. BROWN VIBRATING SCREEN Filed Sept. 5,

Dec. 1924. 11,59,237

N. E. BROWN VIBRATI NG S GREEN Filed Sept. 5, 1922 2 Sheets-Sheet 2 fig 5.

I and useful Improvement Screens, of which the following is aspeci- Patented Dec. 16, 1924.

UNITED -STATES 1,519,231 PATENT OFFICE.

NICHOLAS E. BROWN, OF LOS ANGELES, CALIFORNIA, ASSIGNOR TO THE BRAUN COR- PORATION, A CORPORATION OF CALIFORNIA.

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Application filed September 5, 1922. Serial No. 586,118.

To all whom it may concern:

Be it known that I, NIoHoLAs E. BROWN. a citizen of the United States, residing at Los Angeles, in'the county of Los Angeles, State of California, have invented a new fication.

My invention relates to the art of screening material, and more particularly to the use of a vibrating screen for this purpose.

It is a well known fact that the efficiency of screening action is greatly increased in the case of many materials if the screen is given a rapid vibration during the screening operatlon. Several inventors have attempted to utilize an electro-magnet for producing this vibration.

The rincipal object of my invention? is to'provlde a vibrating screen in which the vibrations are produced electri'callyJ Several inventors have attempted to use an alternative current magnet, using the vibrations of alternativecurrent circuit to produce this vibration. A frequency of 60 cycles per second is common throughout the United States and itispractical by energizing a magnet by an electric current from such an alternating electric source to produce a vibration of the screen for each alternation or 120 vibrations per second, in the case of a 60 cycle supply. I have found that this rate of vibration is too high for most types of material. Other inventors have also discovered this fact and have attempted to reducethe number of vibrations by the use of a frequency changer by which the frequency of the electric circuit can be reduced. I have found that excellent results can be obtained from a screen operated on a 60 cycle circuit if the vibrations are reduced to one-half the alternations or, in other words, to 60 vibrations per second.

The principal object of my invention is to provide a vibrating screen which is energized by asource of alternating electric current, this screen being so constructed that one vibration per cycle is produced on the screen.

Further objects and advantages will be made evident hereinafter.

Referring to the drawings, which are for illustrative purposes only,

in Vibratingv Fig.1 is a diagrammatic view of one form of screen equipped with my invention.

Fig. 2 is an elevation partially in section on the plane represented by theline 2-2 of bolt 13 to an arm 14 pivoted at 15 on a magnet 16. The magnet 16 has the form shown in Fig. 3, being formed of punchings and has an armature 17 which is secured to the arm 14. The armature 17 is at all times in close magnetic relationship with the limb 18 of the magnet 16, leaving an air gap 19 between the other limb 20 of the magnet and the armature 17. Any magnetic flux flowing across the air gap 19-tends to pull the armature 17 against the limb 20, this tendency being resisted by a spring 21 adjusted by a bolt 22.

If an alternating current were applied to a coil uponthe magnet 16, an alternating .flux would be produced and an intermittent vibrations is far too rapid for the average type screen. i

In the illustration, a diagrammatic form of screen is shown, the form of screen having nothing whatever to do with this inven-.

tion which relates wholly to themethod of vibrating a screen. This method is best illustrated in Fig; 3, in which two magnets 3Q and 31 are shown, the magnet 30 having an alternating current exciting coil 32 and a direct current exciting coil 33, the magnet 31 having an alternating current exciting coil 34 and a direct current exciting coil 35. Direct current is supplied through wires 36 and 37 current from the wire 37 flowing through the coil 35, through a connecting wire 38, through the coil 33, through a reactor 39 and an adjusting resistance 40. Al-

ternating current is supplied throughwires 50 and 51; current from the wire 50 passing through to the exciting coil 32, through a wire 52 to the exciting coil 34, through a wire 53 to a reactor 1 and from the reactor 54 to the wire 51. 1

It is of course understood that when an alternating current is supplied to the coil 34 and 32, that an alternating flux is set up in the magnets 30 and 31, this fluxinducing an alternating potential in the direct current exciting coils33 and 35. These coils are so connected that at any instant these induced electro-motive forces are opposed to each other, that is to say, the electro-motive force in the coil 35 is in such a direction that it would cause current to flow in one direction in the wire 38, and the electro-motive force induced in the coil 33 in such a direction that it tends to cause a current to flow in the opposite direction in the wire 38. If the coils 32, 33, 34 and 35 and the magnets 30 and 31 were absolutely identical in construction and in electric and magnetic characteristics, these potentials would actually balance each other and no alternatin current would flow in the direct current coi s. Such a balance is practically impossible and the reactor 39 is provided to further limit this alternating cur- .rent, the resistance 40 being provided to I regulate the flow of the direct current flowdue in in the circuit. a

n ractice, I prefer to make the fluxes inby the direct current in each of the magnets 30 and 31 somewhat greater than the maximum fluxes induced by the alternating current exciting coils 32 and 34. As

' a result, I roduce the effect shown diagram- I maximum falling to a maximum on the other matically 1n Fig. 4 in which a a is a zero line; distances along these lines to left and ri ht indicating equal intervals of time.

hen the ma'gnets 30 and 31 are excited by alternating current, a flux is set up across the air gap 19 which may be represented by the lines b-b-bb. It will be noted that this flux will rise on one side of the line to a tance between the ,line 0-0 and aa. 'We

thus have two forces tending to setyup two magnetic fluxes in the air gap 19; one, the uniform fluxes, due to the direct current, and the other, the alternating fluxes, due. to the alternating current. k

Since the pull upon the armature 17 across the air gap 19 is independent in direction and magnitude of the direction of the fluxes, it is evident that with the alternating current excitation only we would have a pullupon the armature 17 which would start at zero and increase to a maximum on one alternation, dying down to zero and increasing at the same maximumkon the succeeding alternation. Or, in other words, we would have a pull or vibration for each of the peaks at on the curve bb-bb. If the fr uency of the alternating circuit were cyc es, we would then have two of these pulls per cycle or 120 vibrations per second.

By superimposing the direct current fluxes upon the alternating fluxes, a somewhat dif ferent condition appears, the result of the fluxes being shown by the line d-ddd of Fig. 1. This line d'-(ldd is the re.-

sultant of the constant direct current fluxes represented by the line C- C plus the fluxes produced by the alternating current indicated by the line b-bb-b. Since in the diagram the magnitude of the direct current fluxes is somewhat greater than the maximum of the alternating current fluxes, 4

it is evident that when these fluxes are in the same direction a total flux is produced Somewhat gr ater than twice the alternating flux and that when 'these fluxes are o'pposed to each other there still remains a small residual flux representing the difference between the direct current flux and the alternating current flux. As a result, considering the'line am as the zero line,

we have a minimum flux ea'and a maximum flux of ya. It is evident therefore that this resultant flux, represented by the line dddd, rises from the magnitude ea to the magnitude ga once per cycle, or, in other words, we would have one vibration per cycle and on a 60 cycle circuit we would have 60 vibrations per second in place of I have found that this lower number of vibrationsproduces a very eificient frequency for vibrating screens.

I claim as my invention:

1. In a device of the character described, the combination of: a screen member; two armatures; means by which each armature vibrates the screen member; two magnets, one placed to attract one of said armatures and the other placed to attract the other of said armatures; two alternating current exciting coils, one placed upon one of said magnets and the other placed upon the other of said magnets; two 'direct current exciting coils, one placed u on one of said magnets and the other paced upon the other ofsaid magnets; means for impressing an alternating electromotive force on each of said alternatingcurrent exciting coils; and meansconnectm sald direct current exclting coils in senes in such a relationship that the alternating electro-motive force induced in one of said direct current excitmg coils by the alternating magnetic flux established by its associatdd alternating current exciting coil is opposed in direction by the alternating electro-motive force induced in the other of said direct current exciting coils by the magnetic flux established by its associated alternating current exciting coil. A

2. A device of the aha-met described as in'claim 1 in which the means for im-t pressing an alternating force on said alternating current exciting coil includes means independent of said magnets and their exciting coils for inserting external-reactance in the circuits of said alternating current exciting coils.

3. A device of the character described as in claim 1 in which a reactor is inserted in series with said direct current exciting coils for the purpose of reducing-the alternating electric current induced therein;

4. In a device of the class described: a

screen member; an armature; means by which said armature vibrates said screen; means for establishing an alternating magnetic flux of a definite fre uency in such a manner that it tends to esta lish a mechanical .pull on said armature for each alternation of said fiux;fand means for superimposing a unidirectional magnetic flux on said alternating magnetic flux for the purpose of reducing or eliminatin alternate pulls of said alternating magnetic flux.

5. In a'device of the class described: a screen member; an armature; means by which said armature vibrates said screen; means for establishing an alternating magnetic flux of a definite frequency in such a manner that it tends to establish a mechanical pull on said armature for each alternation of'said flux; and means for superimposing a unidirectional magnetic flux on said alternating magnetic flux for the pure pose of increasing the pull during the passage of said alternating flux in one direction and decreasing the pull during the passage of said alternating flux in the other direction.

In testimony whereof, I have hereunto set my hand at Los Angeles, California, this 29th day of August, 1922. 

